Automatically operating apparatus for measuring blood pressure

ABSTRACT

An automatically operating apparatus for measuring blood pressure includes a tying-up cuff capable of being inflated, means receiving voltage impulses corresponding to blood pulsations, an amplifier for these voltage impulses, impulse treating members connected behind the amplifier and an electrical operating device which automatically indicates the diastolic and systolic blood pressure during a cuff pressure cycle depending upon Korotkoff impulses. The apparatus is particularly characterized by two impulse treating channels connected in parallel to the outlet of the amplifier. One of these channels has a filter which passes through that frequency portion of the received total signal which contains the Korotkoff impulses, a first impulse forming device being connected behind this filter. The second channel contains a second impulse forming device. These two impulse forming devices change the signals introduced into them into direct voltage impulses which are amplitudinally dependent upon the Korotkoff impulses or the total signal. The outlets of the two impulse forming devices are connected to a comparison device which delivers an impulse to an operating device when the outgoing values resulting from comparing the amplitudes of the outgoing signals of the impulse forming devices, exceed a predetermined value which is characteristic for the appearance of Korotkoff impulses.

United States Patent [72] lnventor [54] AUTOMATICALLY OPERATINGAPPARATUS FOR MEASURING BLOOD PRESSURE 5 Claims, 9 Drawing Figs.

[52] US. Cl... l28/2.05 M [51] Int. Cl A6lb 5/02 [50] Field of Search128/2.05 A, 2.05 G, 2.05 M, 2.05 P, 2.05 Q, 2.05 R, 2.05 S, 2.05 V

[56] References Cited UNITED STATES PATENTS 2,827,040 3/1958 Gilford128/205 A 2,865,365 12/1958 Newland et al. 128/2.05 A 3,101,082 8/1963Steen et a1. 128/205 M 3,126,886 3/1964 Karsh i 1 128/205 M 3,308,8113/1967 Gillette et al 128/205 M 3,405,707 10/1968 Edwards 128/205 M WA 6UP CUFF A COMPRESSOR BAND F/L TE? EECT/F/E l/VTE I J- EGRATOR PrimaryExaminer-William E. Kamm Attorney-Richards and Geier ABSTRACT: Anautomatically operating apparatus for measuring blood pressure includesa tying-up cuff capable of being inflated, means receiving voltageimpulses corresponding to blood pulsations, an amplifier for thesevoltage impulses, impulse treating members connected behind theamplifier and an electrical operating device which automaticallyindicates the diastolic and systolic blood pressure during a cuffpressure cycle depending upon Korotkoff impulses. The apparatus isparticularly characterized by two impulse treating channels connected inparallel to the outlet of the amplifier. One of these channels has afilter which passes through that frequency portion of the received totalsignal which contains the Korotkoff impulses, a first impulse formingdevice being connected behind this filter. The second channel contains asecond impulse forming device. These two impulse forming devices changethe signals introduced into them into direct voltage impulses which areamplitudinally dependent upon the Korotkoff impulses or the totalsignal. The outlets of the two impulse forming devices are connected toa comparison device which delivers an impulse to an operating devicewhen the outgoing values resulting from comparing the amplitudes of theoutgoing signals of the impulse forming devices, exceed a predeterminedvalue which is characteristic for the appearance of Korotkoffimpulses.

DEVICE DEV/CE 14 32/1 A001 r/ VE EV/CE r 1 014F411. s5 kE CE/ VIA/GAUTOMATICALLY OPERATING APPARATUS FOR MEASURING BLOOD PRESSURE Thisinvention relates to an automatically operating apparatus for measuringblood pressure with a tying-up cuff capable of being inflated, a deviceproducing voltage impulses corresponding to blood pulsations, anamplifier for these voltage impulses, impulse treating devices connectedto the outlet of the amplifier and an electrical operating device whichduring a cuff pressure cycle automatically indicates the diastolic andsystolic blood pressure depending upon the so-called Korotkofi impulses.According to this apparatus the voltage impulses corresponding to theblood pulsations contain all information received from the deviceproducing the voltage impulses, including the Korotkoff impulses.

U.S. Pat. No. 2,827,040 describes an automatically operating bloodpressure measuring device of this type which uses a microphone withamplifier distally mounted upon the extremity and determining thediastolic and systolic blood pressure values. In this device thetying-up cuff is connected with outside air by an outlet nozzle and atemperature responsive electrical resistance is located at the outlet ofthe nozzle. Pressure pulsations of the blood vessel are transmitted tothe cuff and provide that air fiows out of the nozzle in rhythm withthese pulsations. This rhythmically cools the temperature responsiveelectrical resistance and thus produces an electrical signalcorresponding to each pulse. This signal is used to provide confirmationwith the pulses received by the microphone, in that the signals receivedby the microphone transmit an impulse to an operating device only if apressure pulsation was measured at the same time. in this way a certaininsensibility of the device to disturbances is attained. This prior artdevice requires a fairly large technical structure to eliminatedisturbing sounds which are not connected at the same time with pressurechanges in the cuff, since, in order to make possible the requirement ofsimultaneousness and thus the possibility of mutual confirmation of thereceived signals, signals received from the microphone must becorrespondingly delayed due to the pneumatic transmission of thepressure impulses and also due to the heat capacity of thetemperaturedependent electrical resistance.

The difference in time between a signal supplied by the microphone andthe corresponding signal supplied by the temper-ature-dependentelectrical resistance, depends upon the location of application of thecuff and of the microphone. Thus it is necessary to either provide afirm connection between the cuff and the microphone orto set therequired delay for each measurement corresponding to locations ofapplication of the microphone and the cuff. This setting is alsonecessary when the strength of the expected pressure pulsations ofdifferent patients is quite different.

As already indicated, when operating this prior art device, thepossibility cannot be excluded that disturbances, such as, for example,the touching of the cuff which will produce an acoustic as well as apressure signal, will be accepted by the device as actuating signals.Furthen'nore, there is the danger that the pneumatic conduit between thecuff and the outlet noule will be bent or that the nozzle opening getsdirty. Despite the comparatively large technical expenditure, this priorart device does not provide adequate safety for eliminating disturbingsounds or the necessary operational security and simplicity in use.

An object of the present invention is to improve prior art devicesthrough the provision of a blood measuring apparatus of the describedtype which provides an extensive security against disturbances, which issimple in operation and inexpensive in manufacture.

Another object is the provision of an apparatus of this type which doesnot require a calibration before each measurement.

Other objects of the present invention will become apparent in thecourse of the following specification.

In the accomplishment of the objectives of the present invention it wasfound desirable to connect two impulses treating channels to the outletof the amplifier. One of these impulse treating channels has a filterwhich lets through that frequency portion of the entire received signalswhich preferably contains the Korotkoff impulses, and a first impulseforming device connected to the outlet of the filter. The other impulsetreating channel has a second impulse forming device. These two impulseforming devices change the signals introduced into them into directvoltage impulses which are amplitudinally dependent upon the Korotkoffimpulses or the total signal. A comparison device is connected to theoutlets of the two impulse forming devices and delivers an impulse tothe operating device when the outgoing values resulting from comparingthe amplitudes of the outgoing signals of the impulse forming devicesexceed a predetermined value which is characteristic for the appearanceof the Korotkoff impulses.

Thus in accordance with the blood measuring device of the presentinvention the control of the outgoing signal of the impulse formingdevice located behind the filter is carried out by the entire signalsupplied by the receiving device. An actuating impulse is transmitted tothe actuating device only when outgoing values resulting from acomparison of these signals exceed a predetermined value characteristicfor the presence of a Korotkoff impulse. The fact that this value isexceeded takes place independently from the amplitude of the signalsupplied by the receiving device. Therefore a calibration of theapparatus, is not necessary any more. For this reason and due to theresulting insensitiveness of the blood pressure measuring apparatus ofthe present invention to scratching and scraping noises, it is possiblefor the patient under certain conditions to keep his clothing during themeasuring under the measuring cuff; thus the measuring can also takeplace through the clothing.

The apparatus of the present invention is rendered still more reliableby connecting behind the filter an impulse integrator with two diodesand behind this a differentiating step device and also when the secondimpulse forming device consists of a rectifying device and a followingcharging step device, the charge of which takes place with a small timeconstant compared to the duration of a pulse and the discharge of whichtakes place with a large time constant compared to the duration of apulse. The impulse forming devices are preferably so constructed thattheir outgoing impulses have opposite poles. The comparison devicepreferably contains a threshold amplifier which receives the sum signalof these outgoing impulses and which is so adjusted that it supplies anactuating impulse only when a predetermined value of the sum signal isexceeded.

The invention will appear more clearly from the following detaileddescription when taken in connection with the accompanying drawing,showing, by way of example only, a preferred embodiment of the inventiveidea.

In the drawing:

FIG. I is a block switch diagram of a blood pressure measuring apparatusof the present invention;

FIG. 2 shows a diagram of a device constituting a part of the apparatusshown in FIG. I and used for working on impulses corresponding to bloodpulsations and Korotkoff impulses;

FIGS. 31: to 33 are diagrams showing the How of voltage as a function oftime at different locations of the apparatus shown in FIGS. land 2.

FIG. 1 shows a tying-up cuff l which can be inflated by a compressor 2.Two manometers 3 and 4 are connected with the interior of the cuff l formeasuring the diastolic and systolic blood pressure. Air carryingconduits leading to the manometers 3 and 4 are provided withelectrically operated valves 5 and 6 which can be used to close the aircarrying conduits and thus hold the diastolic and the systolic bloodpressure.

A microphone 7 is the receiving member for producing voltage impulsescorresponding to blood pulsations (as a total signal). An amplifier 8 isconnected behind the microphone 7. Two impulse treating channels areconnected in parallel to the outlet of the amplifier. One of thesechannels has a band filter 11 which passes a frequency of about l5 to 30Hz. for the Korotkoff impulses. An impulse integrator 12 with two diodesis attached behind the filter 11 and is followed by a differentiatingstep device 13. The other channel has a rectifier 9 and a followingcharging step device 10 with different charging and dischargingconstants. A precise linear treatment within a wide dynamic range takesplace in the two impulse treating channels, particularly a rectificationof the incoming signals transmitted to the channels. The outlet of thecharging step device 10 and the outlet of the differentiating stepdevice 13 are connected with an additive step device 14 the outlet ofwhich is connected with an actuating device consisting of an impulsetreating step device 15 and an actuating amplifier 16. The compressor 2and the valves 5 and 6 are connected with the amplifier 16. The additivestep device 14 serves as a comparison member and in it take place acomparison of the amplitudes of the outgoing voltages of the chargingstep device 10 and the difi'erentiating step device 13. Elements 15 and16 are well known and are described, for example, in US. Pat No.2,827,040.

FIG. 2 shows that the charging step device 10 consists of an amplifier17 and a condenser arrangement connected to its outlet and consisting ofa condenser 18, a charging diode l9 and a discharging condenser 20. Theimpulse integrator 12 contains an amplifier 22, a condenser 23, diodes24 and 25, a charging condenser 26 and a charging resistance 27. Thedifferentiating step device 13 includes a condenser 28 and a resistance29.

The outgoing conduits of the two parallel branches are jointly connectedto the inlet of a threshold amplifier 30 through resistances 21 and 34.The amplifier 30 is so set by a resistance 31 that an outgoing signal istransmitted to the impulse treating step device 15 only when the sumsignal transmitted to its inlet will exceed a previously predeterminedfixed value.

The operation of the described apparatus will now be described,reference being also had to FIGS. 3a to 3g:

When the starting key 32 is actuated, the compressor 2 will startoperating and will inflate the cuff 1. Valves 5 and 6 are still open, sothat the manometers 3 and 4 will indicate pressure in the cufi 1.Microphone 7 receives the blood pulsations, so that an impulse voltagecorresponding thereto is transmitted to the filter l1 and the rectifier9. Initially there will be no signal voltage at the outlet of the filter11 since voltage supplied by the microphone does not contain initiallyany Korotkofi impulses. Therefore, the differentiating step device 13and consequently the additive step device 14 do not supply as yet anoutgoing signal.

When, however, the impulse voltage will contain Korotkoff impulses atthe outlet of the amplifier 8 (point A), then it can have, for example,the flow indicated in FIG. 3a. The heavy lined curve portions correspondto the Korotkoff impulses. The voltage flow at the outlet B of thefilter 11 is indicated in FIG. 3b. FIG. 3b shows that the filter 11 wascaused to oscillate by a Korotkoff impulse and that this oscillation hadterminated before the arrival of a new Korotkoff impulse. FIG. 3c showsthe flow of voltage at the outlet C of the impulse integrator 12. Theintegrator 12 produces a rectification and a summing up 05 the rectifiedvoltage. For that reason, the maximum voltage at the location C issomewhat later than the maximum voltage at the location B. The chargingcondenser 26 which received rectified voltage charge impulses from thecharge diode 25, is used to sum up the rectified voltage. The chargingoperation takes place by the condenser 23 along with the diode 24.Immediately thereafter, a differentiation of this voltage takes placethrough the differentiating step device 13 consisting of the condenser28 and the resistance 29. Then the outgoing voltage of thedifferentiating step device 13 has at location D the flow shown in FIG.3d. The differentiating step device 13 sieves out continuous disturbingvalues which are noticeable at the location C by direct voltagecomponents.

At the outlet of the rectifier 9 having corresponding poles, namely, atthe location E, there is the voltage which flows in accordance with thediagram of FIG. 3e. The following charging step device 10 has a smalltime constant in comparison to the duration of a pulse for the chargingoperation and a large time constant for the discharge operation. This isattained by coupling the outlet of the impulse amplifier 17 to thecondenser 18 through the charging diode 19, so that a quick charging ofthe condenser 18 through the diode 19 will take place when negativevoltage is located at the outlet of the amplifier 17, while when thediode 19 is locked, the condenser 18 will comparatively slowly dischargethrough the discharge resistance 20 which is greater than thetransmission resistance of the diode 19. Thus the voltage at thelocation F will flow as shown in FIG. 3f.

The outgoing impulses of the charging step device 10 and of thedifferentiating step device 13 are superposed or added at the point 33,so that the voltage at the location G will have the flow shown in FIG.3g. The threshold voltage of the amplifier 30 which corresponds to theabscissa of the diagram of FIG. 3g, is so set through the resistance 31that when a Korotkoff impulse appears only a single narrow impulse,which is shown by heavier lines in FIG. 33, is amplified by theamplifier 30 and is then transmitted to the impulse treating step device15; it will fall into the flat rising part of the curve shown in FIG. 3fdue to the quick charging of the condenser 18. If there is no Korotkoffimpulse, then the sum voltage at the location G is always below thethreshold voltage of the amplifier 30.

FIGS. 3a to 3g indicate that an impulse will be transmitted fromamplifier 30 to the impulse treating step device 15 only when thevoltages at the locations D and F in their superposition exceed apredetermined value. When scraping or scratching noises or prepulsesoccur the outlet voltage of filter 11 actually always reaches anamplitude which is smaller than that shown in FIG. 3b, since thefrequency of these disturbing impulses usually deviates from theresonance frequency of the filter 11 and, in that case, the voltage atthe location G will not exceed the swell voltage of the amplifier 30 andthus there is no falsification of the results of measurements.

Since the maximum voltage at the point G can be easily shifted inrelation to the maximum voltage at the point B, it is safe to assumethat the threshold voltage of the amplifier 30 will not be exceeded inthe dropping part of voltage at the location F, so that then noerroneous impulses can take place.

The described blood pressure measuring device of the present inventiondoes not have to be adapted to individual patients since the criten'umfor recognizing Korotkoff impulses is not the absolute value of thevoltage but a value resulting from the superposition of two voltageswhich to a great extent is independent from the amplitude of the voltagedelivered by the receiving member, namely, the microphone 7.

The described apparatus of the present invention has a single-receivingmember so that it is easy to operate and provides a great safety withrespect to disturbing impulses affecting the receiving member.

Investigations which have been carried out have determined on the basisof a series of experiments a characteristic value (the threshold voltageof the amplifier 30) for the appearance of Korotkoff impulses. A seriesof following investigations have shown that the value which has thusbeen determined applies to all patients.

Further treatment of Korotkoff impulses can take place as follows:

When the first diastolic Korotkoff impulse takes place, the impulsetreating stage device 15 will give to the steering amplifier 16 a signalfor closing the valve 5. The diastolic blood pressure is then held inthe manometer 3. If two following Korotkofi impulses take place during apredetermined time period after the first Korotkoff impulse, they willthus confirm the first Korotkoff impulse and, when a third Korotkofiimpulse takes place, the impulse treating step 15 will deliver a closingsignal to the valve 6 through the amplifier 16. During each of thethereafter following Korotkofi impulses, the valve 6 will be opened fora short time, so that after the last Korotkotf impulse, the systolicblood pressure will be indicated by the manometer 4. If, after the lastKorotkoff impulse, no further Korotkoff impulses appear within apredetermined time, the actuating amplifier 16 will transmit a switchoff signal to the compressor 2. Air is then removed from the cuff l byany suitable known means (not shown). The diastolic and the systolicblood pressure have been fed into the manometers 3 and 4 and can beinspected thereon.

lclaim:

1. An automatically operating apparatus for measuring blood pressure,comprising a patients cuff capable of being inflated, means inflatingsaid cuff to diastolic and systolic blood pressure values of the personbeing examined, a member connected with said cuff for producing voltageimpulses corresponding to the Korotkoff impulses, an amplifier connectedwith said member for amplifying said voltage impulses, indicating means,an electrical operating device connected with said amplifier and saidindicating means for automatically indicating diastolic and systolicblood pressure depending upon Korotkoff impulses during a cuff pressurecycle, two impulse treating channels connected in parallel to saidamplifier, one of said channels comprising a filter connected to theamplifier and transmitting frequencies containing Korotkoff impulses,and a first impulse forming device connected to said filter, the otherone of said channels comprising a second impulse forming deviceconnected to said amplifier, the two impulse forming devices changingsignals introduced into them into direct voltage impulses amplitudinallydependent upon Korotkoff impulses and total signal, a comparison deviceconnected with the outlets of the two impulse forming devices, and anactuating device connected with said comparison device, said comparisondevice delivering an impulse to said actuating device when the outgoingvalues resulting from comparing the amplitudes of the outgoing signalsof the impulse forming devices exceed a predetermined value which ischaracteristic for the appearance of Korotkoff impulses.

8. An apparatus in accordance with claim 1, wherein said first impulseforming device consists of an impulse integrator with two diodes and adifferentiating step device connected in series with said integrator.

3. An apparatus in accordance with claim 1, wherein said second impulseforming device comprises a rectifying device for rectifying impulsesemitted by said amplifier and a charging step device connected in serieswith said rectifying device and comprising a condenser charged byappearing Korotkoff impulses with a small time constant as compared tothe duration of a pulse and a resistance connected with said condenserfor the following discharging of said condenser by a time con stantlarge as compared to the duration of a pulse.

4. An apparatus in accordance with claim 3, comprising an amplifier anda diode, the last-mentioned amplifier and said diode connecting saidrectifying device with said condenser, said valve permitting the passageonly of such impulses which have the size of Korotkoff impulses.

5. An apparatus in accordance with claim 3, wherein the polarity of saidrectifying device is such that the outgoing impulses of said impulseforming members have opposed polarity and wherein said comparison devicecomprises a threshold amplifier receiving the sum signal of the outgoingimpulses and set to provide an actuating impulse only when apredetermined value of said sum signal is exceeded.

1. An automatically operating apparatus for measuring blood pressure,comprising a patient''s cuff capable of being inflated, means inflatingsaid cuff to diastolic and systolic blood pressure values of the personbeing examined, a member connected with said cuff for producing voltageimpulses corresponding to the Korotkoff impulses, an amplifier connectedwith said member for Amplifying said voltage impulses, indicating means,an electrical operating device connected with said amplifier and saidindicating means for automatically indicating diastolic and systolicblood pressure depending upon Korotkoff impulses during a cuff pressurecycle, two impulse treating channels connected in parallel to saidamplifier, one of said channels comprising a filter connected to theamplifier and transmitting frequencies containing Korotkoff impulses,and a first impulse forming device connected to said filter, the otherone of said channels comprising a second impulse forming deviceconnected to said amplifier, the two impulse forming devices changingsignals introduced into them into direct voltage impulses amplitudinallydependent upon Korotkoff impulses and total signal, a comparison deviceconnected with the outlets of the two impulse forming devices, and anactuating device connected with said comparison device, said comparisondevice delivering an impulse to said actuating device when the outgoingvalues resulting from comparing the amplitudes of the outgoing signalsof the impulse forming devices exceed a predetermined value which ischaracteristic for the appearance of Korotkoff impulses.
 3. An apparatusin accordance with claim 1, wherein said second impulse forming devicecomprises a rectifying device for rectifying impulses emitted by saidamplifier and a charging step device connected in series with saidrectifying device and comprising a condenser charged by appearingKorotkoff impulses with a small time constant as compared to theduration of a pulse and a resistance connected with said condenser forthe following discharging of said condenser by a time constant large ascompared to the duration of a pulse.
 4. An apparatus in accordance withclaim 3, comprising an amplifier and a diode, the last-mentionedamplifier and said diode connecting said rectifying device with saidcondenser, said valve permitting the passage only of such impulses whichhave the size of Korotkoff impulses.
 5. An apparatus in accordance withclaim 3, wherein the polarity of said rectifying device is such that theoutgoing impulses of said impulse forming members have opposed polarityand wherein said comparison device comprises a threshold amplifierreceiving the sum signal of the outgoing impulses and set to provide anactuating impulse only when a predetermined value of said sum signal isexceeded.
 8. An apparatus in accordance with claim 1, wherein said firstimpulse forming device consists of an impulse integrator with two diodesand a differentiating step device connected in series with saidintegrator.